1. Field of the Invention
This invention relates to an alignment apparatus in which at least one of a mask and a sensitive member is moved relative to the other while an alignment mark on the mask illuminated by non-sensitizing light and an alignment mark on the sensitive member are observed, in order to bring the mask and the sensitive member into a predetermined positional relation. Thereafter the mask is illuminated by sensitizing light to print the pattern of the mask on the sensitive member.
2. Description of the Prior Art
Alignment apparatus of the general type described above may be roughly classified as (1) contact alignment apparatus in which printing is effected with a mask and a sensitive member (hereinafter) referred to as the wafer and for example coated with a photoresist) in intimate contact with each other, as (2) proximity alignment apparatus in which printing is effected with the mask and the wafer spaced apart from each other by 10-20 microns, or as (3) projection alignment apparatus in which an imaging optical system such as a lens, a mirror, an imaging system, etc. is disposed between the mask and the wafer and a mask image is formed on the wafer to thereby effect printing.
The alignment apparatus of the present invention falls in the projection alignment apparatus category and one feature thereof lies in that this apparatus prevents an alignment mark on the mask from being printed on the wafer. Briefly described, the the mark on the wafer is, therefore, protected or preserved because the alignment mark of the mask is prevented from being printed on the alignment mark of the wafer.
In contact alignment apparatus and proximity alignment apparatus, protection or preservation of the mark of the wafer has been done. That is, in U.S. Pat. No. 3,844,655, a sufficient printing light is imparted to the alignment mark portion of a wafer having a negative sensitivity characteristic through the alignment mark portion of a mask, thereby sensitizing the entire alignment mark portion of the wafer and preventing the alignment mark of the mask from being recorded.
This conventional system requires sufficient printing light to be imparted to the alignment mark of the wafer and this leads to disadvantage that the exposure time or the amount of exposure must be increased.
Particularly, where this conventional method is utilized in the projection alignment apparatus, if the imaging optical system is used intact, a mask image of good contrast will be formed on the alignment mark portion of the wafer and therefore, a long exposure time will be necessary to sensitize the entire mark area by applying light even to the portion shadowed by the mask. This procedure is not practical.